Cyclic Resultants

A resultant for Hensel's Lemma

Let R be a complete discrete valuation ring with maximal ideal generated by pi. Let f(X) in R[X] be a monic polynomial with nonzero discriminant Delta(f). Let s >= v_pi(Delta(f)) + 1. Suppose given a factorisation of f(X) in (R/pi^s R)[X] into several factors, not necessarily coprime in (R/pi R)[X]. We lift it uniquely to a factorisation of f(X) in R[X]. This generalises the Hensel-Rychlik Lemma, which covers the case of two factors. We work directly with lifts of factorisations into several factors and avoid having to iterate factorisations into two factors. For this purpose we define a resul…

Lopsided Approximation of Amoebas

The amoeba of a Laurent polynomial is the image of the corresponding hypersurface under the coordinatewise log absolute value map. In this article, we demonstrate that a theoretical amoeba approximation method due to Purbhoo can be used efficiently in practice. To do this, we resolve the main bottleneck in Purbhoo's method by exploiting relations between cyclic resultants. We use the same approach to give an approximation of the Log preimage of the amoeba of a Laurent polynomial using semi-algebraic sets. We also provide a SINGULAR/SAGE implementation of these algorithms, which shows a signifi…

Automorphisms with eigenvalues in $S^1$ of a ${\mathbb Z}$-lattice with cyclic finite monodromy

For any finite set $M\subset {\mathbb Z}_{\geq 1}$ of positive integers, there is up to isomorphism a unique ${\mathbb Z}$-lattice $H_M$ with a cyclic automorphism $h_M:H_M\to H_M$ whose eigenvalues are the unit roots with orders in $M$ and have multiplicity 1. The paper studies the automorphisms of the pair $(H_M,h_M)$ which have eigenvalues in $S^1$. The main result are necessary and sufficient conditions on the set $M$ such that the only such automorphisms are $\pm h_M^k,k\in{\mathbb Z}$. The proof uses resultants and cyclotomic polynomials. It is elementary, but involved. Special cases of …

循环模的弱提升与Serre提升及Auslander对偶的可提升性

Weak and Serre Lifting of Cyclic Modules and the Liftability of Auslander Transposes

本文研究局部环商环上循环模的弱提升与Serre提升性质，给出刻画及张量积保持条件，并加强相关反例与定理，同时探讨Auslander对偶的可提升性。